The present invention relates to an absorption refrigerator including; a cabinet having outer walls and at least one door encasing a low temperature storage compartment and a higher temperature storage compartment, said compartments being separated by a partition wall, and an absorption refrigerating system including an evaporator tube in which a refrigeration medium flows from an upstream end to a downstream end of the evaporator tube, and which evaporator tube comprises a first tube section which is arranged to absorb heat from the low temperature compartment, a second tube section, which is arranged to absorb heat from the higher temperature compartment, wherein the first and second tube sections are connected in series and the first tube section is arranged upstream of the second tube section.
Such absorption refrigerators are commonly used e.g. in recreation vehicles, mobile homes or at homes were AC power supply is not available at all times.
Normally, at the prior art refrigerators of this type, the lower temperature compartment is a freezer, which at modern absorption refrigerators normally is maintained at −18° C.
The low temperature compartment is occasionally denoted freezer or freezer compartment, the higher temperature compartment is occasionally denoted fridge or fridge compartment and the cabinet, comprising the freezer and fridge compartments are occasionally denoted refrigerator, absorption refrigerator or refrigerator cabinet.
The freezer may also accommodate a device for fabrication of ice, often referred to as the ice-maker. The ice maker may in it's simplest form be an ice-cube container but it may also comprise more sophisticated devices with means for automatic water supply and ice harvesting means including mechanical members and electrical heating elements.
The higher temperature compartment is normally maintained at around +5° C. and could be referred to as a fridge compartment.
The evaporator tube may include an upstream tube section, which is dedicated for cooling the ice-maker, if present. Downstream of this ice-maker tube section and in direct connection to its downstream end, an intermediate tube section is arranged for cooling the freezer. Downstream of the freezer section, a downstream fridge section of the evaporator tube is arranged for cooling the higher temperature fridge compartment. At some applications both the freezer and the ice-maker are cooled together by one single evaporator tube section which is arranged upstream of the fridge tube section.
The evaporator may be provided with various types of heat conducting members for conducting heat from the items to be cooled, i.e. the freezer and fridge compartments and the ice maker, to the respective evaporator tube sections. As an example, the ice-maker section of the evaporator may be provided with a heat conducting plate, which is arranged to support the ice-cube container and which conducts heat from the container to the ice-maker section of the evaporator. The freezer and fridge sections may be provided with flanges or baffles, which conduct heat from the air in the freezer and fridge compartments to the evaporator freezer and fridge section respectively.
The evaporator reaches its lowest evaporation temperature at the upstream end. Downstream of the upstream end, the evaporation temperature rises gradually when the cooling medium in the evaporator tub absorbs heat from the ice-maker, freezer compartment and fridge compartment.
A problem at this known type of absorption refrigerator is that it is difficult to achieve a high enough cooling power of the refrigeration system to maintain the freezer compartment at the low temperature which is desired. As mentioned above, it is often desired to keep the temperature in the freezer compartment as low as approximately −18° C. The total cooling power of the absorption refrigerating apparatus is, among other factors such as ambient temperature, limited by the heat transfer capacity of the evaporator, which in turn depends on the total length of the evaporator tube. This length in turn, is limited by the dimensions of the refrigerator cabinet and by the fact that the evaporator tube needs to be designed with a downward inclination over its entire length, from the upstream to the downstream end.
When the absorption refrigerator is installed in an environment of relatively low temperature, for example 10° C., the proportion of operative phases of the absorption refrigerating system is reduced, resulting in an undesirable decrease in the performance of the freezer compartment.
The temperature in the freezer and fridge compartment are normally controlled by turning the refrigerating system on, when lower temperatures are required, and off, when the required temperatures has been achieved, respectively. To be able to achieve the required cooling level in the freezer compartment the refrigeration system, including the boiler, will have to be turned on more often than would be required to achieve the required temperature in the fridge compartment. This will in turn result in a lower temperature in the fridge compartment than preferable, which of course could have a detrimental effect on food stored in the fridge compartment.
At the upstream end of the evaporator tube, the evaporation temperature of the refrigeration medium is normally approximately −30° C. During manufacturing of ice, i.e. during freezing of water in the ice-maker, the ice-maker section of the evaporator absorbs heat from the ice-maker. This heat absorption rises the evaporation temperature of the refrigeration medium so that it, at the entrance of the freezer section of the evaporator tube, is approximately −24° C. and at the exit approximately −20° C. Thus, during manufacturing of ice, the average driving temperature difference between the desired freezer temperature and the evaporation temperature of the refrigeration medium would then be only about 2° C. Such a small driving temperature difference enhances the problems described above.
DE 196 34 687 A1 discloses a refrigerator using a heater in a fridge compartment to raise the temperature in the fridge compartment, when the requirements for lower temperature in the freezer compartments also lowers the temperature in the fridge compartment. This will of course require extra power to drive the heater element and would be a problem, which is accentuated in the case where the refrigerator, at least partly and occasionally is operated using batteries.